Polymer compositions and processes

Abstract

Melt processed articles of improved color and odor can be produced from hydroxyalkanoic acid polymers if they are melt processed in the presence of a temperature stable sulphite salt, and compositions for use in such processes are disclosed.

We claim: 
     
       1. A plastics composition which comprises a microbially produced hydroxyalkyanoic acid polymer and between 0.1 and 1.0% by weight of sulphur in the form of a temperature stable alkali metal sulphite. 
     
     
       2. A composition as claimed in claim 1 in which the polymer comprises hydroxybutyric acid and/or hydroxyvaleric acid residues. 
     
     
       3. A plastics composition which comprises a microbially produced hydroxyalkanoic acid polymer and a temperature stable alkali metal sulphite. 
     
     
       4. A composition as claimed in claim 3 in which the sulphite salt is sodium or potassium bisulphite. 
     
     
       5. A composition as claimed in claim 4 in which 0.1 to 1.0% by weight of sulphur in the form of sulphite is present. 
     
     
       6. A process of making a composition as claimed in any one of claims 1, 2, and 4 which comprises mixing a solution of the salt with polymer and drying. 
     
     
       7. A composition according to claim 1 wherein the amount of sulphite included is sufficient to improve at least one of color and odor of the polymer when melt processed. 
     
     
       8. A process of producing shaped articles from a microbially produced hydroxyalkanoic acid polymer which comprises melt processing the polymer in the presence of between 0.1 and 1.0% by weight of sulphur in the form of a temperature stable alkali metal sulphite. 
     
     
       9. Shaped articles of improved colour and/or odour formed by the process of claim 8. 
     
     
       10. Shaped articles according to claim 9 which contain residual sulphite salt. 
     
     
       11. A process according to claim 8 wherein the amount of sulphite included is sufficient to improve at least one of color and odor of the polymer when melt processed.